1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus that uses a thermal printing head (TPH).
2. Description of the Related Art
A thermal type image forming apparatus includes a thermal printing head (TPH) and a platen roller placed opposite to the TPH. To form a printing nip, the TPH is pressed toward the platen roller by a spring or the like. When a printing medium passes through the printing nip, the TPH prints an image on the printing medium by applying heat to the medium. The platen roller can be used as a main transfer means for transferring the printing medium at a predetermined printing speed. In addition, when a special transfer unit is provided for transferring the printing medium at the predetermined printing speed, the platen roller is rotated by a contact force generated between the printing medium and the platen roller. In this case, when the printing medium is supplied to the TPH and the platen roller, the TPH and the platen roller must be separated from each other. In addition, when printing is performed, the TPH must be pressed toward the platen roller.
To print an image on both sides of the printing medium (that is, duplex printing), two TPHs placed on the opposite sides of the printing mediums may be used, but the price of the image forming apparatus increases when two TPHs are used. Alternatively, duplex printing can be performed by using one TPH and bringing the TPH into opposition with first and second sides of a printing medium, sequentially. In this case, the TPH can be fixed while the printing medium is flipped over, or the TPH can be moved between opposite positions with respect to the first and second sides of the printing medium.